Micro-electro-mechanical (MEMS) is a technology for manufacturing microelectronic devices using semiconductor process. Compared with conventional electro-mechanical devices, MEMS devices have significant advantages of high temperature resistance, small sizes, and low power consumption. For example, a microphone made using MEMS technology is widely used in portable electronic devices because of its small sizes, which is easier to be integrated into ICs, and high sensitivity. Microphone is a transducer for converting an audio signal to an electrical signal. There are mainly three types of microphones according to operational principle, including piezoelectric type, resistance type and capacitive type. The capacitive microphone predominates in the MEMS microphone due to its high sensitivity, low noise, low distortion and low power consumption.
A completed MEMS microphone usually experiences an etch process in its manufacturing processes, so as to form a diaphragm, an electrode plate, an air gap cavity between them. Chinese Patent No. 200710044322.6 discloses a MEMS microphone and a method for manufacturing the same. FIG. 1 illustrates a schematic sectional view of a conventional MEMS microphone. FIG. 2 illustrates a schematic 3D view of the MEMS microphone shown in FIG. 1. Referring to FIG. 1 and FIG. 2, the conventional MEMS microphone includes: an electrode plate 11 on a top surface of a substrate 10 and having air holes therein; a diaphragm 12 under the electrode plate 11, where an air gap cavity 13 is formed between the diaphragm 12 and the electrode plate 11; and a back cavity 14 on the bottom surface and opposite to the diaphragm 12, which makes the diaphragm 12 suspending between the air gap cavity 13 and the back cavity 14.
The operational principle of the conventional MEMS microphone is as follows: the diaphragm 12 suspending between the air gap cavity 13 and the back cavity 14 may sense sound waves to vibrate freely because the back cavity 14 is open, and air therein may come in and go out freely through the air holes in the electrode plate 11. The distance between the electrode plate 11 and the diaphragm 12 changes regularly with the vibration, so does the capacitance formed by the electrode plate 11, the diaphragm 12 and air therebetween. The variation of the capacitance is output in electric signals, thereby converting audio signals into electric signals.
However, the conventional MEMS microphone has the following disadvantages: a great deal of spaces in the substrate is occupied because the MEMS microphone runs through the whole substrate with the back cavity 14 formed by an etching process. Further, the opening size of the back cavity 14 is difficult to be reduced due to the thick substrate, which causes difficulties in scaling-down devices and integrating the MEMS microphone into a semiconductor chip.